1. Field of the Invention
The present invention relates to a method and circuitry for extending the operating time of a capacitive, electrochemical or nuclear power source in an implantable medical device, by activating a step-up DC to DC Converter upon sensing that the power source voltage has decreased to the minimum operating voltage required by the medical device.
2. Description of the Prior Art
A number of new, state-of-the-art, implantable medical devices, such as, a neural stimulator, a pacemaker, a defibrillator, a drug infusion pump, to name a few, are powered by either a rechargeable or a non-rechargeable power source. This power source can be either a large value capacitor, a rechargeable or a non-rechargeable electrochemical cell, or a nuclear cell. One limitation of all these power sources is that eventually their voltage will diminish to the minimum operating voltage required by the electric circuit at which point the device will cease to provide medical therapy. However, there may be a significant electric charge remaining in the power source that cannot be utilized due to limitations imposed by the minimum operating voltage.